In a process for manufacturing a semiconductor device or an LCD substrate, predetermined processing of a substrate is performed while the substrate is sequentially transported by a substrate transport device between a plurality of processing modules provided in a substrate processing apparatus. The substrate transport device includes, for example, a fork for holding a substrate and which is movable back and forth along a base. The base is configured to be rotatable on a vertical axis and vertically movable.
A substrate, held in a reference position on such a fork, is transferred to a reference position of the substrate holding area of a module. The “reference position” herein refers to e.g. a position where the center of a substrate coincides with the center of the holding area of a fork or a module. Thus, a substrate which has been transferred from a module to a reference position on a fork, is transferred to a reference position in the next module.
However, there are cases where a fork receives a substrate from a module at a position displaced from a reference position on the fork, for example, on the occurrence of an earthquake, or when the substrate bounces off the fork upon transfer of the substrate from the module and is caught by the fork at a position largely displaced from the reference position. The bouncing of a substrate is likely to occur when the substrate is lifted up from a substrate holding surface upon transfer of the substrate under tension between the substrate holding surface and a chemical solution which has intruded into the back surface side of the substrate.
If a substrate, held in a position displaced from a reference position on a fork, is transferred to a module, there is a fear of collision of the substrate with the module, or falling of the substrate from the fork during transport. It is therefore common practice to stop the transport of the substrate; and an operator enters the apparatus and performs a work to reset the substrate in the reference position on the fork, or remove the substrate from the fork.
The stopping of the apparatus, the resetting or removal of the substrate and a work to restore the apparatus must be performed by a worker. A heavy burden is thus imposed on the worker. In addition, it takes a certain amount of time to perform such a work and restore the apparatus, resulting in lowering of the operating rate of the apparatus.
Patent document 1 describes a technique which involves detecting a displacement of a substrate which has occurred during transport of the substrate from a first position to a second position, correcting the displacement, and subsequently performing fine alignment. This patent document, however, fails to address the problem of how to transfer a substrate to a normal position in a substrate transport device or in a module when the displacement of the substrate is large, and the technique disclosed cannot solve the problem.